How do I calculate opposite / most distanced coordinates on the earth?

Question

If i get this coordinates:

City Coordinates: 43°52′0″N 18°25′0″E φ Latitude °N, λ Longitude °E (of Map center): (43.8562586, 18.413076300000057)

How do i determine most distant / opposite coordinates on the earth from those coordinates?

Answer 1

For an oblate spheroid model (or a spherical model), you negate the latitude and add $180^\circ$ to the longitude.

Answer 2

Antipodal point Coordinates: 43°52′0″ S, 180-18°25′0″ W. φ Latitude °S, λ Longitude °W (of Map center):